Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
There is known a full-color image forming apparatus of a tandem engine with a plurality of photoreceptor drums. A plurality of the photoreceptor drums are arranged along an intermediate transfer belt. Each photoreceptor drum is provided with a charger, a developing apparatus, a transfer apparatus, a cleaning apparatus with a rubbing roller, and a similar apparatus at a peripheral area. The charger causes a circumference surface of the photoreceptor drum to be charged by a discharge operation. Irradiating light from an exposure apparatus forms an electrostatic latent image at the circumference surface of the photoreceptor drum charged by the charger. The developing apparatus develops the electrostatic latent image formed at the circumference surface of the photoreceptor drum as a toner image. The transfer apparatus transfers the toner on the developed photoreceptor drum to a target transfer member. A blade or a similar tool of the cleaning apparatus scrapes off toner remaining on the photoreceptor drum that has not been transferred. By rotation of the rubbing roller in contact with the circumference surface of the photoreceptor drum, the toner that has not been transferred polishes the circumference surfaces of the respective photoreceptor drums. Thus, the rubbing roller shaves off a foreign object such as corona products adhered to the circumference surface of the photoreceptor drum.
The developing apparatus supplies (transfers) toner to the circumference surface of the photoreceptor drum requiring polishing by the rubbing roller among the plurality of photoreceptor drums. The toner contains a polishing-agent. Interaction of the polishing-agent and the rubbing roller polishes the circumference surface of the photoreceptor drum. The developing apparatus arranged at the peripheral area of the photoreceptor drum usually supplies toner to the circumference surface of the photoreceptor drum. Besides, for example, the developing apparatus located at an uppermost stream in a conveyance direction of an intermediate transfer belt among a plurality of developing apparatuses may supply toner to the photoreceptor drum requiring polishing. In this case, the intermediate transfer belt is used as a toner supply unit.
The image forming apparatus of tandem engine includes respective developing apparatuses accumulating toners with respective different colors. Among them, since the developing apparatus accumulates a toner with color of low usage frequency (printing rate) over a long period of time, deterioration of such toner proceeds faster than other toners by stirring in the developing apparatus or a similar operation. The deteriorated toner will be one cause of image quality deterioration of a printed image. Accordingly, a typical image forming apparatus performs a development refresh control to forcibly discharge deteriorated toner in the developing apparatus when an image is not formed.